Question

Let $\frac{C}{5}=\frac{F-32}{9} .$ If $C$ lies between $10$ and $20$, then :

• A. 50 < F < 78
• B. 50 < F < 68
• C. 49 < F < 68
• D. 49 < F < 78

Answer 1

Answer: (B)

Given $: \frac{C}{5}=\frac{F-32}{9}$ and $10 < C < 20$
$\Rightarrow C =\frac{5 F -(32) 5}{9}$
Since, $10 < C < 20$
$ \Rightarrow 10 < \frac{5 F -160}{9}<20$
$\Rightarrow 90 < 5 F -160 < 180$
$ \Rightarrow 90+160 < 5 F < 180+160$
$\Rightarrow 250 < 5 F < 340$
$ \Rightarrow \frac{250}{5} < F < \frac{340}{5}$
$\Rightarrow 50 < F < 68$